Direct current (DC) subsystems supply power to DC relay subsystems in electrical utility substations, and therefore, are a critical component in the operation of the substations. DC subsystems convert alternating current (AC) power to DC power for use in operating the DC relay subsystem and provide uninterrupted power to DC relay systems in the case of a loss in AC power or a brownout. Uninterrupted power is provided by batteries, which are maintained and monitored by other modules in the DC subsystem.
Regular diagnostic testing of DC subsystems is critical to reliable operation. In addition, new North American Electric Reliability Corporation (NERC) standards require more frequent inspection and testing of DC subsystems. In DC subsystems of the prior art, a technician must visit each physical substation location and typically perform tests by manually connecting test equipment to various components of the DC subsystem. Due to the potential for injury, such tests must be performed by a highly-trained technician at significant cost to the operator of the substation. Accordingly, there is a need for DC subsystems that enable diagnostic tests to be performed and reviewed by technicians with a wider variety of levels of skill and experience.